The Most Important Threat to Survival of Polar Bears at This

The most important threat to survival of polar bears at this time is

A) ocean currents delivering pollutants to the Arctic Ocean from oceans in more temperate climate zones
B) hunting by native populations
C) tourism disruptions
D) warming of the frozen Arctic, which has has caused the winter ice pack to shrink and break up earlier, thus limiting hunting opportunities for the bears
E) a normal population cycle that will result in their slow extinction